The manufacture of microelectronic semiconductor devices has become increasingly miniaturized. This miniaturization has provided notable improvements in microchip performance, while reducing the cost of the fabricating materials. Such advantages in cost and performance, however, are not without drawbacks. The higher electronic component densities of these microchips has increased the difficulty of their fabrication. Manufacturing yields of high-density microchips tend to decrease proportionately with higher electronic component densities. Thus, there is a continuing need for new, high-yield processes for etching the microchip materials and/or depositing films on their surfaces. A major objective of every manufacturer is the continual improvement of the yields for the individual fabrication steps used to make the microchip.
It has recently been discovered that etchant admixtures containing molecular chlorine, Cl.sub.2, can be used at great advantage in the fabrication process. The improvement in the etching reaction is believed to be partly due to the ability of the chlorine atoms to stabilize and regulate the aggressive etching characteristics of fluorine atoms.
When plasma-etching silicon, a fluorine-containing compound in admixture with chlorine gas has been found to provide good selectivity in accordance with the teachings in U.S. Pat. No. 4,310,380, issued to Flamm et al on Jan. 12, 1982. The admixture in the described process has been used successfully to control lateral undercutting.
Similarly, in U.S. Pat. No. 4,214,946, issued to Forget et al on Jul. 29, 1980, there are illustrated selective polysilicon etchant processes, utilizing a mixture of sulfur hexafluoride with chlorine, which is diluted with an inert gas. Sulfur hexafluoride admixed with chlorine provides an improvement over wet chemical etching, as well as plasma etching for sub-micron-sized lines having extremely close tolerances.
In U.S. Pat. No. 4,264,409, issued to Forget et al on Apr. 28, 1981, still another etchant comprising diluted chlorine and an inert gas admixture containing silicon tetrafluoride is described for the purpose of providing a highly selective etching process. Such a process is claimed to produce vertical sidewalls on the etched features, hence producing no mask undercuts. The process also eliminates the surface contamination associated with using the conventional etchants, carbon tetrafluoride or sulfur hexafluoride.
Chlorine admixtures have also been found to be advantageous in the deposition or growth of thin films. U. S. Pat. No. 4,746,549, entitled "Method for Forming Thin Film of Refractory Material", issued to Ito and Moriya on May 24, 1988, illustrates a method for selectively depositing a refractory metal, using a refractory metal halide admixed with hydrogen and chlorine. Further, U.S. Pat. No. T954,009, entitled "Method for Thermal Oxidation of Silicon with Added Chlorine", issued to Malin and Seybold on Jan. 4, 1977, demonstrates a film growth process which provides improved electrical properties for gate oxides used in field effect transistors.
Despite the improvements cited in the aforementioned patent processes, however, contamination and corrosion can easily be introduced with the addition of a chlorine gas admixture. Contamination and corrosion must be avoided, if high manufacturing yields are to be maintained. Hence, the chlorine is often diluted with inert gas to reduce the contaminating and corrosive effects. Unfortunately, the dilution of the chlorine also decreases, to some extent, its advantageous characteristics; therefore, a balancing of the chlorine gas and inert gas is usually necessary. This balancing act tends to produce unpredictable results, which often further limits the ability to provide high yields.
Another disadvantage of these chlorine admixtures is their introduction of complexities into the etching chemistries. The reaction complexities are primarily due to the increased number of reactants in the admixture necessary to practice the invention. This increase tends to add variability to the etching process; hence, there is often a decrease in process reproducibility, yield and throughput.
The present invention seeks to maintain the advantages provided by the chlorine admixtures, while eliminating or greatly reducing the aforementioned disadvantages.
The current invention comprises contamination-free selective etching and/or film deposition and growth, using new, low-energy, chlorine-containing etchants. The new etchant molecules have a distinct advantage over the prior art. Since reaction rates are good, heating of the electronic materials is minimized and device junction depths better controlled. Radiation damage to the electronic materials is also minimized, since the plasmas of the invention utilize a simplified, low-energy, interhalogen reaction. In addition, yields are maximized, since corrosion or contamination is eliminated or greatly reduced. Unlike their more energetic counterpart plasmas, the low energy of activation by which these molecules provide useful etching and/or film growth and deposition creates improvements in process throughput, as well as manufacturing yield.
The present invention utilizes a new family of etchants. The new etchant family features a single molecule containing a nitrogen atom and both fluorine and another halogen atom consisting of either chlorine or bromine. The size and constitutents of the etchant molecule provide for good reaction stoichiometry. On activation, the etchant molecule conveniently dissociates into only volatile species, without the formation of contaminant by-products.
The invention can be introduced during the formation of thin film structural layers of the chip, i.e., during deposition and growth processes. The invention can likewise be introduced after the formation of thin films of electronic material on the microchip surface, as when an apertured mask is used to selectively etch given areas of a thin film.